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Erdős problem 890

A question of Erdős and Selfridge [ErSe67], who observe that lim inf⁡n→∞∑0≤i<kω(n+i)≥k+π(k)−1\liminf_{n\to \infty}\sum_{0\leq i < k}\omega(n+i)\geq k+\pi(k)-1 for every kk. This follows from Pólya's theorem that the set of kk-smooth integers has unbounded gaps - indeed, n(n+1)⋯(n+k−1)n(n+1)\cdots (n+k-1) is divisible by all primes ≤k\leq k and, provided nn is large, all but at most one of n,n+1,…,n+k−1n,n+1,\ldots,n+k-1 has a prime factor >k>k by Pólya's theorem.

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890.lean

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A question of Erdős and Selfridge [ErSe67], who observe that lim inf⁡n→∞∑0≤i<kω(n+i)≥k+π(k)−1\liminf_{n\to \infty}\sum_{0\leq i < k}\omega(n+i)\geq k+\pi(k)-1 for every kk. This follows from Pólya's theorem that the set of kk-smooth integers has unbounded gaps - indeed, n(n+1)⋯(n+k−1)n(n+1)\cdots (n+k-1) is divisible by all primes ≤k\leq k and, provided nn is large, all but at most one of n,n+1,…,n+k−1n,n+1,\ldots,n+k-1 has a prime factor >k>k by Pólya's theorem.

FormalConjectures/ErdosProblems/890.leanErdos890.erdos_890.variants.liminf_lower_bound3 linesExact file
∀ (k : ℕ),  Filter.liminf (fun n => ∑ i ∈ Finset.range k, ↑(ArithmeticFunction.cardDistinctFactors (n + i))) Filter.atTop ≥    ↑k + ↑k.primeCounting - 1
SolvedStatement only, no proof